BIOHYDROGEN FROM CHEESE WHEY TREATMENT IN AN AnSBBR: ACHIEVING PROCESS STABILITY

An AnSBBR (anaerobic sequencing batch reactor containing biomass immobilized on an inert support) with liquid phase recirculation, containing a 3.5 L working volume, treated 1.5 L of cheese whey wastewater in 3 and 4 h cycles at 30 °C to produce biohydrogen. From startup the bioreactor presented process instability. To overcome this problem the following measures were taken, however without success: adaptation of the biomass with uncontaminated easily degradable substrates, pH control at very low levels, and a different form of inoculation (natural fermentation of the feed medium). The problem was solved by cooling the feed medium to 4 °C to prevent acidification in the storage container, by eliminating nutrient supplementation to prevent possible formation of H2S by sulfate-reducing bacteria and by periodic washing of the support material to improve the food/microorganism ratio. Hence, stable hydrogen production could be achieved with minimal presence of methane (36% H2; 62% CO2; 2% CH4) and the AnSBBR fed with cheese whey (influent concentration of 4070 mgCOD.L and 3240 mgCarbohydrate.L and applied volumetric organic loading of 14.6 gCOD.L.d) presented improved productivity and yield indicators compared to pure lactose and other reactor configurations, reaching values of 420 NmLH2.L.d and 0.60 molH2.molCarbohydrate in the steady-state phase (conversions of carbohydrates and COD were 98% and 30%, respectively).